1. Field of the Invention
This invention relates to night vision viewing systems.
More particularly, the invention relates to night vision viewing systems of a kind suitable for support on headgear to provide a wearer of the headgear with an intensified view of a scene ahead of the wearer superimposed on and in register with the wearer's direct view of said scene.
2. Description of Related Art
A known such system comprises an eyepiece arranged to intercept a forward line of sight of an observer using the system, and an optical sub-system including a forward-looking objective lens fixed with respect to said eyepiece and having an optical axis offset with respect to said forward line of sight, and an image intensifier means disposed optically between said objective lens and said eyepiece so that light rays of an intensified real image of a scene forward of the observer viewed by said objective lens are directed into said eyepiece via an input surface thereof which faces upwardly with respect to said forward line of sight, thereby to provide the observer with a view of said intensified image which is superimposed on and in register with the observer's direct view of said forward scene through said eyepiece.
Such a night vision viewing system is hereinafter referred to as a night vision viewing system of the kind specified.
It will be appreciated that whilst a night viewing system of the kind specified gives the observer a monocular view only of the distant scene, two such systems may be used, one for each eye of the observer, to provide a binocular view. Moreover, the two such systems may, at least in part, share a common optical sub-system so that the observer is provided with a biocular view only.
Known night vision viewing systems in which the system is supported on headgear have certain inherent shortcomings when used in environments such as the cockpit of a high performance aircraft. Inevitably the centre of gravity of the night vision system is at a position forward of the neck pivot position of the headgear wearer. The weight of the night vision system is, generally speaking, of the order of 1 kg; and, heretofore the moment arm about the neck pivot position has been around 13 cms. In static conditions therefore the user must develop a balancing torque of about 1.3 newton meters. Under high gravitational force manoeuvre conditions any unbalanced mass of quite small magnitude may constitute a danger to the wearer.